Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Generating sinusoidal output
Reexamination Certificate
2000-06-26
2002-03-12
Lam, Tuan T. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Generating sinusoidal output
C327S106000
Reexamination Certificate
active
06356124
ABSTRACT:
FIELD OF THE INVENTION
The disclosure relates to a method and an apparatus for generating digital sine wave signals. In particular, the systems disclosed and described relate to simplified systems for generating variable frequency sine wave signals for use in communications applications.
BACKGROUND OF THE INVENTION
Many electronic applications and systems require the use of sinusoidal signal generators that may be digitally sampled. Often, such sinusoidal signal generators are used in communications applications, such as for use in mixing or tone generation. Further, other varied uses of sinusoidal signal generators exist.
Many electronic applications require that the frequency of the sinusoidal signal being generated is selectively variable. As depicted in
FIG. 1
, selectively variable frequency sinusoidal signals may be generated using a system such as system
10
that includes a look-up table
12
having a frequency input
14
to provide a waveform output
16
. The frequency input provides a clock signal at the desired frequency and look-up table
12
is used to retrieve a memorized sample of the frequency associated sinusoid from a look-up table or data table. The data table may be stored on any type of storage device, commonly in a read only memory (ROM) stored table. Because it may be impractical to store sinusoid samples from a large number of frequencies, the frequency accuracy and distortion performance may be poor. Such performance may be improved by storing large amounts of samples, which translates into substantial amounts of chip real estate, that is used up by ROM.
Referring now to
FIG. 2
, a system for providing a sinusoidal waveform output
20
is depicted. System
20
includes a selective frequency input
22
, a look-up table
24
, an interpolation mechanism
26
, and a waveform output
28
. Similar to system
10
, frequency input
22
supplies a clock signal to look-up table
24
. Look-up table
24
retrieves stored samples of sinusoidal signals from a data table. The data table may be stored in any of a variety of storage devices, most commonly ROM. Because sample values at each clock tick of a desired frequency may not be available in the data table, an interpolation mechanism
26
interpolates sample values between points that are not included in the data table. Because, the look-up table requires numerous sample values and the interpolation mechanism requires a plurality of calculations, the complexity of system
20
is undesirable. Further, system
20
requires a set of sample values and derivative values in the data table for each of a plurality of frequencies.
Referring now to
FIG. 3
, a system
30
for generating a selective frequency sinusoidal signal is depicted. System
30
includes a selective frequency input
32
, a recursive calculations device
34
, and a waveform output
36
. A selective frequency input is applied to the recursive calculations device. The recursive calculations device uses a pair of difference equations as its staring point, therefore some initial conditions must be input to the recursive calculations. Because system
30
does not use a look-up table, no ROM is required and therefore, may be seen as the smallest implementation in respect to die area (i.e. the area required on an integrated circuit device or other electronic device layout). However, recursive system
30
is very sensitive to initial conditions and requires calculations to be carried out with large numbers of decimal places, to provide appropriate accuracy. The algorithm complexity is usually far beyond an easy hardware implementation and typically requires a microprocessor or a digital signal processing (DSP) device including a floating point array. The recursive system
30
however is capable of providing accurate frequency setting and performance.
Accordingly, there is a need for an alternative method and apparatus for generating sinusoidal signals. There is a need for a method and apparatus for generating accurate sinusoidal signals in a wide frequency band that may be fit into a relatively small die area. Further, there is a need for a method and system for generating sinusoidal signals that may be used in communication systems and devices which maintain relatively good accuracy and require few and simple computations.
SUMMARY OF THE INVENTION
An exemplary embodiment relates to a signal generator. The signal generator includes a variable frequency selector. The variable frequency signal is configured to provide a variable frequency signal. The signal generator also includes a periodic signal generator. The periodic signal generator is configured to generate a periodic signal. The periodic signal generator has an input receiving the variable frequency selection and an output providing the periodic signal. The periodic signal has a frequency approximately the same as the variable frequency selection. The periodic signal generator is configured to store a table of derivative values associated with a reference periodic signal, each stored derivative value corresponding to a discrete time in the reference periodic signal. The periodic signal generator is configured to interpolate between the discrete points in the table of derivative values.
Another exemplary embodiment relates to a periodic signal generator. The periodic signal generator includes a programmable clock divider having a frequency select input and a master clock frequency input. The programmable clock divider has an output providing a clock frequency signal. The periodic signal generator also includes a periodic function generator. The periodic function generator has an input receiving the clock frequency signal, and the periodic function generator has an output providing a periodic function signal having a frequency substantially the same as the frequency of the clock frequency signal. The periodic function generator stores a data table of rate of change values associated with a reference periodic function. Each stored rate of change value corresponds to a discrete time in the reference periodic signal. The periodic function generator is configured to interpolate between the discrete points in the data table.
Yet another exemplary embodiment relates to a method of generating a periodic signal having a selectively variable frequency. The method includes receiving a frequency select signal by a variable frequency clock. The method also includes receiving a master clock signal by the variable frequency clock. Further, the method includes providing a selected frequency signal by the variable frequency clock, to a periodic function generator configured to generate a periodic signal of variable frequency. Further still, the method includes retrieving a rate of change value from a stored data table of rate of change values associated with the periodic signal. Yet further still, the method includes calculating a new value of the periodic signal using an interpolation based on the retrieved rate of change value from the data table of values.
REFERENCES:
patent: 5016259 (1991-05-01), Hershberger
patent: 5936438 (1999-08-01), Whikehart et al.
patent: 6121816 (2000-09-01), Tonks et al.
Conexant Systems Inc.
Foley & Lardner
Lam Tuan T.
LandOfFree
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